NMR spectroscopy experiments

Higher magnetic fields exist tiian those used in NMR but the NMR experiment imposes constraints in addition to just magnitude. An NMR spectroscopy experiment also demands homogeneity and stability of the magnetic... 

The assembly formation of heterobidentate ligated complexes was studied in detail using bidentate ligand 13"b as a typical example (Figure 8.8). UV/Vis titrations and NMR spectroscopy experiments showed that the pyridyl moiety of b selectively coordinates to thezinc(ii)porphyrinl3withabindingconstantofK(ib) = 3.8x lO m. An increase in the Kfor 13 b to 64.5 X lO was observed in the presence of metal... 

These experiments, based predominantly on isotopic labeling and kinetics, and related observations cemented the notion of complexes with coordinated C—H bonds as intermediates (i.e., metal/CH o-complexes) during C—H activation and C H elimination processes, and they set the stage for more detailed studies of C H activation mechanisms. The indirect inference of o-complexes based on isotopic labeling experiments has been supported by spectroscopy including fast IR experiments and specialized NMR spectroscopy experiments. Section 11.4 provides an overview of these experiments. 

Spin-state selective experiments have been an integral part in both the history and development of NMR spectroscopy. Experiments vary from the early simple double-... 

A strength of the distance geometry approach is that the conformation generation process can be augmented with experimental data (e.g., interatomic distances), which have been derived from 2D NMR spectroscopy experiments. The generated structures will then fulfill the observed conformational restrictions. 

On the basis of this, two-dimensional (2D) NMR spectroscopy experiments can be defined as experiments that involve one time domain for signal evolution (fi) and an additional time domain for detection and signal acquisition (t2) together with appropriate radio-frequency... 

Derivation of biological macro molecular structure by NMR spectroscopy involves the application of a variety of multidimensional NMR spectroscopy experiments, many of which are beyond the scope of this chapter. Nevertheless, there are some basic principles and ideas that the chemical biology reader should be aware of, which we shall attempt to cover. These basic principles and ideas pull very heavily on the discussion in Main Sections 5.3 and 5.4 above. In brief, the structural characterisation of a biological macro molecule by NMR spectroscopy draws upon a similar approach in every single case. The key objectives are the following. 

Multinuclear NMR spectroscopy experiments of various 1,3-dialkylimidazolium ILs dissolved in organic solvents have also pointed to the formation of floating aggregates through hydrogen bonds [81-84]. In particular, it has been demonstrated by heteronuclear NMR experiments on [C4CjIm]BF4 that contact ion pairs exist in the presence of small amounts of water and even in dimethyl sulfoxide (DMSO) solution [85]. 

Bertini 1, Duma L, Felli IC et al (2004) A heteronuclear direct-detection NMR spectroscopy experiment for protein-backbone assignment. Angew Chem Int Ed 43 2257-2259... 

Fig. 9 NMR spectral changes revealed by a 5 mm solution of hyperpolarized choline upon undergoing phosphorylation by 0.5 units of choline kinase, (a) Emergence of the new phosphocholine resonance shown by directly detected single-pulse N NMR spectroscopy experiments, (b) Emergence of the H NMR resonance associated with the methylenes in the C2-position of phosphocholine, (c) Comparison between the expected enzyme kinetics of kinase with results afforded by the N- ( ) and H-detected ( ) hyperpolarized experiments, as derived from the relative peak ratios of the NMR peaks in (a) and (b). The straight line illustrates the best fit of the combined set of data points, and corresponds to an initial phosphorylation rate of 0.3 mM min under these conditions. Reproduced with permission from [55]...

Courchay et al. [57] conducted a series of NMR spectroscopy experiments to better understand the effect of allylic methyl groups in CM. Under both ADMET and CM conditions, [Mo]2, [Ru]l, and [Ru]2 showed significantly reduced conversion with substrates containing an adylic methyl group. In the case of [Mo]2, an accumulation of the nonproductive metallacyclobutane was observed, while both Grubbs catalysts coordinated the substrate only to yield nonproductive metathe-... 

Solving 3D structures of membrane proteins is a great challenge because of the difficulty in finding well-behaved model membranes. Bicelles are well suited to overcome these difficulties and enable the use of SS MAS NMR spectroscopy experiments for studies on a large soluble domain containing a low concentration of membrane protein cytochrome b5 at... 

Band-selective NMR spectroscopy experiments are really useful for peptides and proteins because a set of equivalent spins (amide NH, H , or aliphatic side-chain protons) appear in well-separated regions. Another alternative to obtain PS-HSQC spectra is by implementing the HOmodecoupled Band-Selective (HOBS) detection scheme [73,74]. This technique has been successfully implemented in a suite of NMR experiments involving IP H magnetization, such as Inversion-Recovery and CPMG-Project experiments... 

NMR spectroscopy of enols has been a key tool in determining the relative proportions of keto and enol forms in highly enolized species. For example, in pentane-2,4-dione, the keto and enol forms (Figure 17.7) can be readily identified in the NMR spectrum of the material the keto-enol tautomerism is slow compared with the timescale of the NMR spectroscopy experiment. This experiment has been extended by changing the temperature, which allows the calculation of thermodynamic parameters for the equilibrium, and the use of a range of solvents to study the effect of polarity. The process has also been studied in the gas phase, where enols predominate for almost all p-dicarbonyl compounds. In solution, the keto forms are generally some 8-9 kj moH more stable than in the gas phase. 

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